Let's Make Robots!

Will this motor driving even work?

Hey guys!

fritsl had a blog post about motor driving and h-bridges and it seemed what he basically needed was to "flip the voltage" and get the motor to change its rotation the other way around.

Now I've been thinking a little about it and came up with something that looks like a half-bridge but is really something that in my mind will allow a motor to rotate in both directions and coast. Only problem is that I'm not sure if it will work at all - so I'm asking you guys to either verify that it's a sane design or that it is just way out there before I test it and maybe blow up the house :-).


The idea is that when the upper transistor is on and the lower is off there will be a voltage drop of 3V across the motor in one direction and when the upper transistor is off and the lower is on there will be a voltage drop of 3V across the motor in the other direction. Shouldn't that be all right?

- Jimmy

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Where is Chuck in this?

And JKA; Good to hear from you again - how's your bot comming up?

Sorry, guys, I am always off topic on your threads, lol!

/ Frits

I had to spend easter with the family, so not much time for building. Hope to get some time soon. Why weren't you at the robot club meeting yesterday? We were only 6. If people don't start showing up, I'm afraid that Prosa might cancel the meetings.
Being down with the flu and nothing better to do, I created a small test setup. I used 5V/2.5V input, a voltmeter instead of a motor and switches instead of transistors. The 2.5V input was created with a voltage divider made out of two 100K resistors (they were the first ones I found; I didn't give much thought to the values). It seems to work. When I press switch one, I get around 2.5V and the other switch I get -2.5V. I don't know how much power you can draw from this setup, though, but as a small experiment it's nice.

Thanks for doing the experiment :-). I guess there won't be coming much power through 100K resistors but the voltages could be created using voltage regulators and for small motors that setup should work fine. Too bad about the flu but now you have time to experiment with robots ;-).

- Jimmy

Geez, I just forgot that in order to output three different voltages from the microcontroller you would probably need some more circuitry that would just make the whole thing a lot more complicated than the standard H-bridge :-)

- Jimmy